This invention relates to a rotary vane pump, and, more particularly, to a silencer-carrying rotary vane pump suitably used as an oilless rotary vane pump.
The known silencers for the sound of a fluid in a vacuum pump inlcude a silencer formed of, for example, a space in a case for a pump driving motor as shown in, for example, Japanese Utility Model Laid-Open No. 165269/1983, or a sealed dead space around the outer circumferential surface of a shaft coupling provided between a pump driving motor and a pump as shown in, for example, Japanese Patent Laid-Open No. 88485/1983.
However, in these prior art silencers, no consideration is given to the reduction of the frictional sound, which is one of the causes of the noise in a rotary vane pump, of the vanes slidingly moving along the inner circumferential surface of a pump casing.
An object of the present invention is to minimize the above noted problems of noise in conventional techniques, especially, the frictional sound of the vanes in a rotary vane pump, and thereby provide a lower-noise rotary vane pump.
The characteristics of the present invention reside in that a hollow portion is provided between the inner and outer circumferential walls of a cylindrical center case of a rotary vane pump, which hollow portion is closed with side covers to form a sealed chamber, through which a pumped out medium is discharged to the outside. This structure enables the sound of a flow of the pumped or discharged medium to be minimized, and the sealed chamber to be utilized as a soundproof layer for preventing the propagation of the frictional sound of the vanes which are slidingly moved along the inner circumferential wall of the center case of the pump. This makes it possible to provide a lower-noise rotary vane pump.